In addition to the insulation of vibrations, which is also provided by conventional rubber elements, the hydro bushings include a damping characteristic for damping the vibrations occurring in the vehicle between the engine and the chassis. As described with respect to FIG. 7, the damping characteristics are achieved with a system integrated into the hydro bushing. This system comprises a support spring, which acts as a piston, and a channel. Here, the mass in the channel and the volume stiffness form a vibration-capable system.
Such systems are matched to approximately 10 Hz and are therefore able to compensate for the inherent vibrations of the engine. Conventional standard hydro bushings are completely unsuited for damping in the lower hearing range.
The invention is directed to a hydro bushing which can filter out acoustic disturbing noises, especially in the region of approximately 130 Hz.
United Kingdom patent application 2,192,968 (corresponding to U.S. patent application Ser. No. 888,595, filed Jul. 23, 1986) is directed to comparatively large vibration amplitudes in the region of the inherent frequency of the damping system as well as to high frequency vibrations of comparatively small amplitude. For attenuating low frequencies of large amplitude, there are two volume-changeable chambers which are connected to each other via a transfer channel as in a standard hydro bushing. Additionally, a further gas chamber for taking up high frequency vibrations of low amplitude is provided and this gas chamber is closed off with an elastic membrane, that is, here, in the acoustic range, only small amplitudes can be filtered out. A further disadvantage is that additional measures are required for damping the expanded range. The manufacture with respect to these measures is associated with additional complexity.